Illusion's DIY Trailer

[Paul H (admin)]

Some good sun today let me start on Illusion's trailer, which will be a hybrid of Ratcatcher John's old trailer hacked to pieces Sweeny Todd style plus some new bits.

It will be bolted together based upon 25mm box section steel. Here is the early work on the axle with 250kg suspension units:





-Paul

[Paul H (admin)]

Unseasonably warm weather for February (12C) allowed some more progress on the trailer.

Here is the mock-up with 3m lengths of 25mm box section, deliberately overhung to hold a rear roller for Illusion's flat bottom:





The idea is that by lifting the trailer the roller can scoop up the bow without putting the bearings in the water. The box section wall is 2.5mm thick to keep the weight down:





Everything bolts together, I could easily extend the axle for a wider boat. After testing with Illusion I moved the long lengths on top of the axle to keep the roller further away from the road:





-Paul

[Anders]

Nice thread. Keep them comming. Unfortunately, where I live (Spain) they´ll never allow me to use something like that.

[Chris Waite]

Paulie

Is 25 mm box section going to be sturdy enough?  I have just stripped down an old trailer and it has box of 30 x 50 mm.  Mine is actually a small T-frame laid long dimension horizontally overtopped with a 25 (?30) mm angle rectangle to support a ply base and plank sides; despite the ply and sides, the angle had managed to crack immediately behind the axle due to fatigue.  I realize that box is much stronger than angle, but might a triangular frame like yours benefit from the deeper measurement vertically?

Chris W

[Jeremy]

I've built a few trailers now, with each getting a bit better, based on experience gained from the ones before.  My latest trailer build was a bolt and rivet together aluminium alloy one (you can perhaps spot a theme here.....) and I would amplify the concerns that Chris has expressed about the section of the tubes.  Wall thickness isn't critical, but section width is, as trailers seem to be dominated by stiffness requirements, rather than strength.

If you want to use the 25mm box, then you might want to look at adding two shorter lengths at the point of maximum bending stress (centred on the axle).  If you were to fit a couple of short (say half the length of the bits you've already got) to the other side of the axle frame, then bolt the ends up to the long lengths with some suitable spacers and long bolts, you would retain the lightness but massively increase the stiffness.  The key to making structures like this stiff is to space the material that's doing the work as far apart as you can get it, either by using bigger section tubes or by fabricating a stiff girder from a couple of bits of smaller stuff.

My first boat trailer was a commercially made T type one, with a hinged section that carried the rollers to ease the task of getting the boat on and off.  It was for a 3/4 ton boat and the long arm was made from 4" square tube.  Despite this big section the trailer would flex quite a lot, the only fix was to lash the bow of the boat down hard to allow the hull to stiffen up the whole trailer.

I've designed the trailer for my electric Winsome (which also uses 250kg suspension units like yours) to allow a bit of flex.  It uses a cradle and support at the bow to  effectively let the hull stiffen up the trailer and seems to work well (it towed well on the trip from Cardigan to Salisbury).  The main member on my trailer is 2" square, 1/8" wall box section, with a short section of 1 3/4" square, 1/4" wall box section inserted inside as a bolt support, to prevent local crushing where the hitch, jockey wheel and bow post are bolted on.  The diagonal members that run back to the axle on either side are made from 2" x 1" x 16g tube.  I can probably wheel the trailer outside and take some photos if you want to nick some ideas from it.

Jeremy

[Paul H (admin)]

Jeremy, Chris,

Thanks for your comments.

Ratcatcher John's Mirror trailer that I based this design on used 25mm box section up to the hitch and 35mm angle for the axle.

It had a plate welded onto the "arms" at the point of maximum stress where the suspension units bolted on (I'll post a pic tonight). So Jeremy's suggestion sounds good, if I understood it correctly.

Illusion is designed to be 250Kg fully displaced - I'm 70kg, subtract 30kg for the water ballast ideas we have and she will never be more than 150kg out of the water....and currently only about 30kg. I tested it yesterday with me and wifey standing on the axle and I could not see any flex in the axle, only along the length towards the hitch (total test weight is of course top-secret ).

As the long arms are now on the top I could build up a 75mm deep beam section either side of the axle. Does that sound right Jeremy and can I use stainless 8mm bolts?

Maximum stress is I think on the forward bolts under tension as they apply the moment to balance the turning moment of the suspension units. I dislike anything other bolt material as they rust but I might settle for high tensile galvanised with stainless nuts. The top/bottom beam idea also spreads the turning load each side onto 2 bolts.

cheers
Paul

[Jeremy]

I don't think you'll see too much flex in the axle tubes, I suspect it'll be the trailer keel that flexes a bit, based on my experience.  Every trailer I've owned (one bought and three built) has had some flex in the keel, one required some additional beefing up because the flex made the trailer bounce a lot on the road.

I use stainless bolts and have never had a problem.  The suspension units on my trailer are held on with them, as were the last two, and I've never had a failure.  They are fairly lightly loaded, so should be fine.

Here are some photos of my current trailer that might give you some food for thought.  It's all bolted/riveted together:









Jeremy

[Paul H (admin)]

Jeremy,
 
Thank you for the pictures of your trailer - she is well built, I'd give you 9/10 if I was your metalwork teacher! (metalwork was my favourite at school, 94% in the O-level coursework).
 
It's a while since I did moments in A-level maths but can you check over this picture please. Moments M1 and M2 are equal at rest, so there is a tremendous reduction in the peak bending force on the arms with a box section underneath. Of course you knew all that!




I have two offcuts of 1300mm box section to bolt underneath - I wonder if they should be fitted asymmetrically towards the front (as shown in picture) because maximum stress is probably during towing?

cheers,
Paul

[Jeremy]

Thanks for the kind words, Paul.

That sketch is exactly what I had in mind, with the extra bits offset towards the front, as you suggest.  As you've already found, the improvement in stiffness will be pretty significant.  Although a little bit of flex in the longitudinal members is probably a reasonably good thing, as I discovered with a trailer a few years ago, too much can make it bounce around a lot when towing over bumpy roads.  The trailer I had with this problem used to hit resonance on some surfaces and just set up a really violent vertical oscillation, that could only be stopped by slowing right down.

Jeremy

[Ratcatcherjohn]

Good evening Paul                With all the usual caveats i.e.  "Agricultural Construction"  and "Harry Clagg from Rent- a- Welder", I would think twice about drilling holes to bolt the lower short section to the A-frame.  A couple of plates top and bottom and two bolts, hard against the A-frame sides may be a possible alternative  soloution.  Alternativly I do have a welder sat in my shed which is looking for a good home ( Lorrain tells me it is looking for any home good or otherwise). 
Then there is the "Third Way".   Parked in the field next to my shed is a ready made trailer and it only bent a little bit with TBA sat on it.......... and   yes, you may have guessed, Lorrain says it is looking for a good home!!!
 
Regards  John
 

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Date: Mon, 7 Feb 2011 13:00:08 -0800
From: [hidden email]
To: [hidden email]
Subject: Re: Illusion's DIY Trailer

Thanks for the kind words, Paul.

That sketch is exactly what I had in mind, with the extra bits offset towards the front, as you suggest.  As you've already found, the improvement in stiffness will be pretty significant.  Although a little bit of flex in the longitudinal members is probably a reasonably good thing, as I discovered with a trailer a few years ago, too much can make it bounce around a lot when towing over bumpy roads.  The trailer I had with this problem used to hit resonance on some surfaces and just set up a really violent vertical oscillation, that could only be stopped by slowing right down.

Jeremy

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[Paul H (admin)]

Jeremy,

To stop MilliBee bouncing the solution was simply to winch the bow tightly to the bow snubber. Also a turnbuckle pulls the bow vertically down onto the angled snubber. With everything locked down there is no movement at all. She rests on her bilge cases - ideally there would be a keel rubber towards the bow but its too high and difficult to fit one.

With Illusion it will be easy to add a keel rubber and clamping her to the post should make the whole assembly rigid.

John,
Illusion is fairly light at the moment and won't get heavy if I can make water ballast work. So we'll see how it goes, but all points noted. I like the fact that the trailer is light and it won't be difficult to strengthen the trailer in the future. It's like the fun of Mecanno, bolt on a bit more to stop it wobbling!

On the subject of welding, I just wish I could find an evening class on gas/TIG for some serious stainless welding.

cheers all,
Paul

[Port-Na-Storm]

A Trailer tale.

Before my Whilly Tern went off to The Netherlands it was on a perfectly serviceable galvanised T trailer.



The buyer asked it was CE type approved as this is a legal requirement over there, to which I replied we still weld old bedsteads together.  He didn't laugh but bought an enormous thing which would have happily carried a Dreadnaught.


Please don't ask why I have an Umbrella sticking out of my head it had been a very long day, and I'm here to tell you Timmo you can't get from Calais to Ammersfoort in 4 hours.
I was stopped at UK customs on the way back who asked why I was towing an empty boat trailer.  I didn't have the nerve to say "oh bugger where's my boat?"  

Personally I think we over engineer everything and for our lightweight boats I'd prefer something like these, only with the load slung low between the wheels.


http://www.sportsrig.com/

Now I have this idea, I've got a couple of spare 2 by 2's and some old bike wheels and I was thinking .........

[Paul H (admin)]

Port-Na-Storm wrote

Now I have this idea, I've got a couple of spare 2 by 2's and some old bike wheels and I was thinking .........

Graham,

I have two pairs of these if you want to build a 4x4 version.....

[Ratcatcherjohn]

Paul       Although it goes against all my Agricultural training, I do like the concept of a fairly light "Ladder frame" trailer (Possibly utilising a bit of an aluminium ladder?) to which you secure the boat in such a way that it is the inherent rigidity of the boat that provides the rigidity to the trailer.  Half a dozen big ratchet straps, suitably located and well graunched down and she should ride for ever. 
It will probably involve putting in a couple or so extra bulkheads to take the resulting compression forces but there just may be a couple of spare sheets of 18mm marine-ply in my shed   -- Cherry faced at that -- which if doubled up should do the job and look nice as well.  Sorry, I forgot, you weigh your component parts, it would, however, save on water ballast.  So we get right back to "The Third Way" and a ready made trailer sat in the field next to my shed.
 
John
 
 

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Date: Mon, 7 Feb 2011 14:23:00 -0800
From: [hidden email]
To: [hidden email]
Subject: Re: Illusion's DIY Trailer

Jeremy,

To stop MilliBee bouncing the solution was simply to winch the bow tightly to the bow snubber. Also a turnbuckle pulls the bow vertically down onto the angled snubber. With everything locked down there is no movement at all. She rests on her bilge cases - ideally there would be a keel rubber towards the bow but its too high and difficult to fit one.

With Illusion it will be easy to add a keel rubber and clamping her to the post should make the whole assembly rigid.

John,
Illusion is fairly light at the moment and won't get heavy if I can make water ballast work. So we'll see how it goes, but all points noted. I like the fact that the trailer is light and it won't be difficult to strengthen the trailer in the future. It's like the fun of Mecanno, add a bit more to stop it wobbling!

On the subject of welding, I just wish I could find an evening class on gas/TIG for some serious stainless welding.

cheers all,
Paul

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[WalneyJohn]

Hi Paul,
for what it's worth, I have a standard combination trailer for my Laser dinghy. The Trolley & Trailer both have 27mm Square section longitutionals, but the axle beam is 3" angle. The boat only weighs 60kg, although it feels much heavier  after a days sailing

regards,
John

[Jeremy]

Paul,

The resonance problem I had was caused by the torsional load that the suspension units place on the cross beam "axle", which twisted the keel tube slightly every time the wheel went over a bump.  No matter how hard I tied the bow of the boat down it persisted, until I stiffened up the trailer keel much as in your sketch.  I was a bit leery of tying the centre of the boat to the trailer keel, because it would have applied a bit of an odd load to the hull.

If you look at where the loads are applied from the wheels, as you've shown in your diagram, you can see how this twist arises; it's a fundamental property of these Indespension type suspension units and can be pretty high when the trailer hits a bump (expect around 4g  minimum, so 4 times the static load).  It's also the primary reason for the two diagonal members on my latest trailer.  A basic T shape would be fine for all the normal static and horizontally applied towing loads, as there's not much force trying to move one wheel fore and aft relative to the other.  Those diagonals are torsion braces, restraining the suspension units from twisting the cross beam by transferring the twisting moment to a point further up the trailer keel.

Jeremy

[Paul H (admin)]

Jeremy wrote

If you look at where the loads are applied from the wheels, as you've shown in your diagram, you can see how this twist arises; it's a fundamental property of these Indespension type suspension units and can be pretty high when the trailer hits a bump (expect around 4g  minimum, so 4 times the static load).  It's also the primary reason for the two diagonal members on my latest trailer.  A basic T shape would be fine for all the normal static and horizontally applied towing loads, as there's not much force trying to move one wheel fore and aft relative to the other.  Those diagonals are torsion braces, restraining the suspension units from twisting the cross beam by transferring the twisting moment to a point further up the trailer keel.

For those reasons I went for the wider axle design - two 25mm box sections across the 110mm wide suspension units.

With the beam like strengthening we discussed the arms should be strong, so I hope the axle sections are not weakened by the 8mm holes ......if the axles flex too much I could easily switch to 30x30 or 40x40 sections, but I salvaged plenty of 25mm box section from Ratcatcher John's trailer and I'm too mean not to re-use it! (aka Scrapheap Challenge )

-Paul

[Randonneur]

Hi Paul,
I see that an Enigma clone has just been finished and is ready for sea trials over on the yahoo microcruising group.



Pete

[Paul H (admin)]

Pete + all that have seen Illusion,

Thanks for that Pete.

I like the long cabin but the vertical edges look a bit "boxy" for me. Something curved or angled would suit me better.

Rowing will be a challenge with that design, but maybe a Yuloh is the way to go.

Also I need to get my weight fully to the gunnels to balance the rig (without ballast) so can anybody suggest or sketch a better cabin shape?  

-Paul

For reference: Elusion's cabin is more curvy:

[Paul H (admin)]

Almost finished, with the beam section Jeremy suggested, 2ft x 2ft of wood covered in carpet will be centred over the axle to support Illusion's flat bottom:




Illusion can slide back so that the combined centre of gravity is over the wheel's axle, easily balanced by one finger during launch/recovery. The rear overhang supports Illusion:





For towing she will be tied forward as usual:





Hopefully it will be ready for a test drive next week, then the Hamble on Sunday the 20th with a mid-day high tide.

cheers
Paul